Some types of electronic circuits use relatively little power, and produce little heat. Circuits of this type can usually be cooled satisfactorily through a passive approach, such as conduction cooling. In contrast, there are other circuits which consume large amounts of power, and produce large amounts of heat. One example is the circuitry used in a phased array antenna system.
More specifically, a modern phased array antenna system can easily produce 25 to 30 kilowatts of heat, or even more, and thus requires about 25 to 30 kilowatts of cooling. Existing systems for cooling this type of circuitry utilize an active cooling approach, in which a fluid coolant is circulated. Existing cooling systems of this type will leak coolant at potential leakage sites, and leakage of coolant may be cause for the system to be shut down. A more recent approach, which can better handle newer circuitry that produces larger amounts of waste heat, involves a cooling system that uses boiling heat transfer, including a system where the pressure in the coolant loop is below the ambient pressure in order to promote boiling at lower temperatures. One advantage of this latter type of system is that, since the cooling loop is at a subambient pressure, the coolant does not have a tendency to leak out of the loop. Although existing units of this type have been generally adequate for their intended purposes, they have not been satisfactory in all respects.
For example, in the case of a subambient cooling system with a two-phase coolant, the coolant does not tend to leak out of the loop, but gases such as air from the ambient environment that may leak into the loop and become present in the coolant can decrease the cooling capability of the system. Existing systems of this type lack the capability, during system operation, to remove air that has leaked into the system's closed loop so as to ensure full capacity operation while eliminating the need to shut the system down for maintenance.